Organic EL display devices, which include an organic EL element which utilizes electroluminescence (hereinafter referred to as “EL”) of an organic material, have been attracting much attention as all-solid-state flat panel displays having excellent properties in terms of low voltage drive, fast response characteristic, self-light emission property, wide viewing angle characteristic, and the like.
An organic EL display device has a configuration in which, for example, an organic EL element is provided on a substrate, which is constituted by a glass substrate or the like and is provided with a TFT (thin-film transistor), and the organic EL element is electrically connected with the TFT.
The organic EL element is a light-emitting element capable of emitting light with high luminance by low voltage DC drive, and has a structure in which a first electrode, an organic EL layer, and a second electrode are laminated in this order.
Known examples of methods for designing an organic EL display device including such an organic EL element to have full color display include (1) a method for arranging organic EL elements, which emit red (R) light, green (G) light, or blue (B) light, as pixels on a substrate, and (2) a method for combining organic EL elements which emit white light with color filters so as to select color of light to be emitted from individual pixels.
The organic EL element is a self-luminous element which emits light in all directions, and is almost a point light source. Furthermore, a gap is formed when attaching a substrate on which the organic EL element is formed by vapor-depositing and a color filter substrate to each other. Consequently, emitted light leaks between adjacent pixels, resulting in color mixture.
FIG. 6 is a cross sectional view illustrating a conventional organic EL display device. In the organic EL display device illustrated in FIG. 6, a color filter substrate (CF substrate) on which a black matrix and color filter layers (CF) are provided is positioned to face a TFT substrate on which white organic EL layers are provided.
White light emitted from a white organic EL layer right below a red CF(R) passes through the red CF(R) and becomes red light, thereby contributing to red display. However, a part of light which is emitted from the white organic EL layer travels in a direction not in parallel with a normal to a color filter substrate 20 and passes through a green CF(G), thereby becoming green light. Furthermore, white light emitted from a white organic EL layer right below a blue CF(B) passes through the blue CF(B) and becomes blue light.
Since the green light forms an incident angle with respect to the CF layer, the green light is mixed with the blue light, resulting in decrease in display quality.
Patent Literature 1 describes a technique in which light-shielding members are provided at a sealing space between an element substrate and a transparent sealing substrate (color filter substrate) so as to prevent color mixture due to leakage of light between adjacent pixels.
FIG. 7 is a view illustrating a cross sectional structure of an organic EL display device disclosed in Patent Literature 1. As illustrated in FIG. 7, the organic EL display device disclosed in Patent Literature 1 has light-shielding members having a height substantially equal to a distance between a transparent sealing member and a second electrode, thereby preventing light transmitted by the second electrode and emitted therefrom from reaching adjacent pixel regions.
Furthermore, Patent Literature 2 describes that a semiconductor oxide such as zinc oxide is used instead of a silicon semiconductor film used for a TFT. FIG. 8 illustrates an example of a cross sectional view of a TFT 900 including a semiconductor oxide layer described in Patent Literature 2.
A semiconductor oxide layer 907a of the TFT 900 is connected with a source line 913as and a drain electrode line 913ad via openings 911as and 911ad, respectively, of an insulating film 909.
A semiconductor oxide layer 907b of an auxiliary capacitor Cs is connected with an auxiliary capacitor electrode (herein, drain electrode 13ad) in an opening 911b of the insulating film 909 and is connected with a pixel electrode 919 in an opening 917b of a protecting film 915.
The TFT using the semiconductor oxide has higher electron mobility, allowing drive with a smaller TFT. This allows designing a high-definition panel with a smaller pixel size.